Infection, especially mediastinitis, is major complication in cardiac surgery. Considering that cardiopulmonary bypass (CPB) can alter kinetics of drugs, including antibiotics, the aim of this study was to evaluate the influence of cardiopulmonary bypass ( CPB) on plasma concentrations and pharmacokinetics of cefuroxime, administered prophylactically, in a 1.5g dose, followed by three bolus of 750mg every 6 hours, for 24 hours, in 19 patients undergoing coronary artery bypass graft (CABG) with CPB (CPB Group, n = 10), or without CPB (Off-Pump Group, n = 9); and assess whether the proposed dosing regimen is adequate to maintain plasma concentrations above 16 g/L (4 times the MIC) for the first 24 hours after the beginning of surgery.